The letters, from CEOs Felicia Thornton and Jim Gooch, which went to warehouse and office workers, said "We are writing one final time, to invite you to return to work and perform your job obligations."

The letters were first posted to social media sites and then confirmed as authentic for our sister station WCVB in Boston by a Market Basket manager.

For workers who do not return to work, "the company will consider you to have abandoned your job, thereby ending your employment with the company," the letter said. Some 200 employees received the letter, Market Basket said.

The letter was sent only to those employees that have failed to report to work at Market Basket headquarters and distribution center.

The letters arrived the day after three independent Market Basket board members called again for the supermarket chain's protesting employees to return to work, and customers to return, and said they are available to negotiate an end to a battle over control of the company.

"We must end this zero sum game and act in the best interests of our Associates, customers - and in the end, our company. We are ready to meet. It's time," the three directors said in a statement Monday.

The directors said last week they had proposed that fired CEO Arthur T. Demoulas and his management team return, without taking control, to assist a return to normal operations as talks continue on his bid to buy out other family members who own a majority of the company. Demoulas, through a spokeswoman, rejected that as a "disingenuous" attempt to have him stabilize the company while they consider selling it to another bidder. Demoulas had offered Aug. 3 to return as CEO during the talks.

On Sunday, he said in a statement issued by a spokeswoman that his offers to buy Market Basket "have been rejected, not on the basis of price, but with counterproposals that have been laden with onerous terms that are far beyond comparable transactions."

Demoulas was fired in June by a board controlled by his rival cousin, Arthur S. Demoulas.

The power struggle has led to protests by thousands of employees and a boycott by customers, leading to a steep drop in sales at the chain with 71 stores in Massachusetts, New Hampshire and Maine.

The shareholders aligned with Arthur S. Demoulas - the current head of the board - said they were willing to accept the purchase price offered by Arthur T. Demoulas, but added that he was unwilling to accept financing for the deal that was secured by collateral and that included a reasonable payment schedule.

The offer for the private company has not been disclosed, but an industry publication estimates the company's value at up to $3.5 billion.

Arthur T. Demoulas said his offer was made at a "pre-crisis" valuation of the company. His spokeswoman said he hopes the rival family faction will reach an agreement "before it is too late to save this company."